Mixturopoda evansi, Baker, Anne S. & Monson, Frank D., 2007

Baker, Anne S. & Monson, Frank D., 2007, Mixturopoda Baker and Monson, a new genus of the uropodine family Metagynuridae (Acari: Mesostigmata) from the British Isles, Zootaxa 1665, pp. 1-17: 4-14

publication ID

http://doi.org/ 10.5281/zenodo.180061

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scientific name

Mixturopoda evansi

sp. nov.

Mixturopoda evansi  sp. nov. ( Figs. 1–27View FIGURES 1 – 2)

Type material

Holotype female: ENGLAND, South Lancashire, Formby, Marsh Farm (grid ref. SD 287059View Materials), up to c. 1 metre inwards from open edge of Dutch barn, ex. damp rotten straw down to depths of 15cm, coll. F.D. Monson, 10 August 2004. Paratypes, same data as holotype: 16 females, 6 males and 3 deutonymphs mounted in Hoyer’s medium, 9 females and 2 males preserved in alcohol [deposited in the Natural History Museum, London; acc. no. BMNH (E) 2007 - 50]; 4 females, 2 males and 1 deutonymph mounted in Hoyer’s medium, 6 females preserved in alcohol [deposited in Entomology Section, Liverpool Museum, UK]; 2 females and 2 males mounted in Hoyer’s medium [deposited in second author’s personal collection].

Female (10 specimens measured).

Yellow –mid brown in life, moderately sclerotized.

Idiosoma. Length 333 (310–365), width 168 (155–183); shield integument foveate ( Figs. 14, 15View FIGURES 14 – 18), minutely pitted between foveae (visible under light microscope); sclerotized cuticle between shields finely striated; setae short, fine, mostly smooth and spiniform ( Fig. 16View FIGURES 14 – 18).

Dorsal shield ( Figs. 1View FIGURES 1 – 2, 14, 16View FIGURES 14 – 18): covering entire dorsal surface, undivided, anterior margin narrowly rounded, anterolateral margins with two concavities (forming shoulders at c. 0.15 and 0.3 from anterior limit), lateral margins approximately parallel, posterior margin widely rounded; with a shallow furrow running longitudinally on either side of median area (not obvious in slide-mounted specimens); foveae slightly smaller and sparser in area between fourth and eighth pair of median setae; with c. 46 pairs setae; j 1 weakly bifid (tines not always discernible; in some specimens these setae appear thicker than the others, Fig. 16View FIGURES 14 – 18 shows thickening is due to adhering material), 5–8 long; 2 posteriormost pairs weakly spinose (as in Fig. 26View FIGURES 25 – 27), curvature prevents precise measurement, but apparently greater than 20 long; remaining setae 5–12 long, generally increasing in length from anterior to posterior; 11 pairs poroids.

Ve n tr al surface ( Figs. 2–4View FIGURES 1 – 2, 15View FIGURES 14 – 18). Pedofossae and scabellum absent. Tritosternum: base large, broader than long, roughly rounded triangular –pentagonal; single lacinia, tapering, sparsely pilose. Sternal shield: foveae less numerous and mostly smaller than on genital and ventrianal shields; fused with endopodal shields, delimited from metapodal elements by short metapodal line posterior to coxae IV; posterior margin slightly concave, accommodating anteromedian margin of genital shield; with 4 pairs sternal setae, st 1–3 8–10, st 4 6–7 long; 1 pair poroids, located approximately level with anterior margins of coxae II. Exopodal and metapodal shields: fused; ornamentation like that of sternal shield; large metapodal elements extending to posterior margin of genital shield; 2 setae located on posteriormost part of metapodal shields, 6–8 long; 3 pairs poroids present, located near margin lateral to area between coxae III and IV, lateral to midpoint of coxae IV and near metapodal line. Genital shield: roughly semicircular, slightly concave anterolaterally; hinged along posterior margin ( Fig. 3); anterior limit almost reaches posterior margins of coxae IV, length 56 (53–61), greatest width (between posterolateral angles) 113 (105–118); genital setae st 5 located medially near posterior margin, 10– 12 long. Endogynium comprising small, elongate median sclerite flanked by two globose structures. Ventrianal shield: roughly semicircular, margin posterior to anus curving dorsally; length 53 (49–63), greatest width (between anterolateral angles) 131 (123–145); 4 pairs preanal setae, anterolateral pair c. 8 long, others 10–12; paranal setae 12–14 long, inserted c. level with posterior limit of anus; anus bordered anteriorly and laterally by inverted U-shaped sclerite. Marginal shield: narrow, extending round idiosoma from c. midpoints of coxae II; separated from dorsal shield by narrow suture; posterior part bearing 4 pairs setae, increasing in length posteriorly from 9–14, plus single postanal seta posterior to midpoint of anus, 6–7 long. Peritremes straight, not convoluted, extending to or just past anterior margin of coxae I; stigmata located laterally to midpoint of coxae III; peritrematic shields fused to exopodal shields and to dorsal shield anteriorly, bearing 1 seta near posterior margin of coxa I and 1 near middle of coxa II.

Gnathosoma ( Figs. 5–8View FIGURES 4 – 8). Gnathotectum: free margins of base strongly and irregularly serrated, slanting to long, slender, weakly pilose central prong. Hypostome and basis gnathosomatica: corniculi robust, acuminate, short, not reaching past distal margin of palp femur; anterior and internal posterior hypostomatic setae spiniform, the former thicker, c. 6 and 7–8 long respectively, external posterior hypostomatic seta slender, clearly longest (15–18), palpcoxal seta thickened, with c. 6–8 tines, 7–8 long; hypognathal groove with 3 rows of small, variably sized denticles, each row comprising c. 3–5 denticles; internal malae serrated laterally. Palp: setal complement 2-5 - 4-10 - 13; trochanteral setae v 1 and v 2 located respectively basally and apically on ventrodistal tubercle, v 1 short, spiniform, v 2 long (reaching between distal limits of palp genu and tibia), basal part thick with c. 3 spicules, remaining part slender, tapering; femoral setae spiniform, al thickest; genual seta al spiniform, remainder slender, absent seta interpreted as d 3, dorsal lyrifissure near proximal margin; 2 dorsodistal setae of tibia clearly the longest; tarsus with large bifid apotele, proximal posterolateral seta noticeably longer than other setae. Chelicera: dorsal seta spiniform, c. 3 long; fixed digit 20–23 long, with 1 backwardly-directed subterminal tooth and 3 antiaxial sensilla-like structures, proximal clavate, distal bulbous, ventral spiniform; movable digit 16–18 long, with 1 subterminal tooth (2 proximal minute serrations also seen in some specimens); lateral lyrifissure, pilus dentilis and sclerotized node on levator tendon not observed.

Legs ( Figs. 9–15, 17, 18View FIGURES 9 – 11View FIGURES 12 – 13View FIGURES 14 – 18). Lengths - I 115 (110–123), II 147 (138–164), III 122 (115–133), IV 144 (135– 155); coxa I with conspicuous antiaxial basal pore with rounded valve, in some specimens a second, smaller pore (not shown) is suggested c. level with distal seta on one or both legs; leg II slightly thicker than others; lateral and dorsal integument of genu –tarsus I tuberculate-pusticulate, rough on other podomeres and legs, ventral surfaces smooth; distal lateral margins of podomeres weakly to strongly serrated; peripodomeric fissure of femur I complete, that of II –IV incomplete; tarsus I with only ventral element of peripodomeric fissure present, otherwise fissure complete; basitarsi II –IV with dorsodistal flap overlying base of telotarsus, posterodorsal pore-like structure present at base of flap, dorsal lyrifissure of telotarsus just distal to or under limit of flap. Ambulacrum absent from tarsus I, that of II –IV comprises two claws and 1 rounded diamond-shaped ventral and 2 obovate dorsal pulvillar elements, distolateral margins of pretarsal sheath acute. Setae: simple, mostly spiniform although thickness and length vary, many on femora –tarsi inserted on small papilla, dorsals generally shorter than ventrals. Setal complements and chaetotaxy: coxae 2 - 2 - 2 - 1; trochantera 4-5 - 3 - 3, al of I shorter and thicker than other setae; femora - I 1-2 / 1-2 / 2 - 1, II 2 - 2 / 1-2 / 1 - 1, III 1-2 / 1 - 1 / 1 -0, IV 1-2 / 1-2 / 1 -0, al 2 of basifemur II minute, other basifemora without setae; genua (positions of some setae on II –IV difficult to assign) - I 1 - 1 / 1 - 1 / 1 - 1, II 2-3 / 2 - 1, III 2 - 1 / 0-1 / 0-2, IV 1-2 / 1 - 1 /0-0; all tibiae 1 - 1 / 1-2 / 1 - 1; tarsus I with 23 tactile setae (acuminate, apart from 1 apical spatulate anterolateral), 1 posterolateral subterminal hollow receptor and terminal cluster of 5 hollow receptors (central one bulbous, antero- and posterolaterals slender, dorsal and ventral ones inflated), tarsi II –IV 3 - 3 / 2 - 1 / 1-2 / 2-3, with al 3 of II and pl 3 of III –IV slightly thicker and clearly shorter than other basitarsal setae, cuticular structure just posterior to pore-like structure on basitarsi II –IV hypothesized to be alveolus of missing seta pd 3, telotarsi II –IV with al 1 and pl 1 long and slender.

Male (9 specimens measured)

Idiosoma. Length 295 (280–315), width 163 (155–168).

Ve n tr al surface ( Figs. 19View FIGURES 19 – 22, 25View FIGURES 25 – 27). Sternogenital shield: ornamentation on anterolateral extensions and along endopodal elements of leg II and III comprising a few very small foveae, central part between anterior margin and posterior margin of coxae II with larger sparsely distributed foveae, a pair of anteromedially curved sculpture lines beginning at level of posterior margin of coxae II and slanting to anterior margin of genital orifice, with 4 pairs setae, st 1 and 2 8–10 long, st 3 and 4 7–8; genital orifice located between coxae IV, covered by anterior circular and posterior crescent-shaped shields, greatest width of posterior shield c. 15. Metapodal shields: fused to ventrianal shield, but not sternogenital shield; lacking setae. Ventrianal shield: median area extending anteriorly almost to genital orifice (outline of anterior margin sometimes irregular), expanding in posterior half to acute lateral angles; with 8 pairs setae, paranals located c. midway along anus, genital setae st 5, antero- and mediolateral pairs 5–6 long, posterolateral and 2 median pairs 9–11, lateromedian pair 7–9, paranals 13–15; 3 pairs poroids, associated with st 5, anterolateral and lateromedian setal pairs.

Gnathosoma. Hypostome and basis gnathosomatica: anterior and internal posterior hypostomatic setae 3– 4 and 3–5 long respectively, external posterior hypostomatic seta 13–15, palpcoxal seta c. 7. Chelicerae: fixed digit 16–18 long, movable digit 14–15.

Legs ( Figs. 20–22View FIGURES 19 – 22, 25View FIGURES 25 – 27). Lengths - I 109 (100–115), II 136 (125–145), III 116 (110–123), IV 134 (128– 140); II slightly thicker than in female, femur with greatly enlarged seta av (appears trispinate in some views), tarsus curved, terminates in greatly enlarged claw-like structure interpreted as seta av 1, chaetotactic interpretation as in Fig. 21View FIGURES 19 – 22, av 2 and mv thickened, elbowed near base, md thorn-like, ambulacrum displaced posterolaterally; pv 1 of tarsus III and IV enlarged, hooked apically.

Free -living deutonymph (5 specimens measured)

Yellow –very pale brown in life, lightly sclerotized.

Dorsal idiosoma ( Figs. 23View FIGURES 23 – 24, 26View FIGURES 25 – 27). Setae j 1 clavate, located on striated cuticle anterior to dorsal shield, c. 3 long. Dorsal shield: length 286 (260–305), width 146 (138–163); less extensive than in adults, precise outline variable; with 30 pairs setae, 2 posteriormost pairs c. 20–24 long, remainder 6–8. Setae of 15 marginal pairs each borne on small platelet (some of which may be contiguous).

Ve n tr al surface ( Figs. 24View FIGURES 23 – 24, 27View FIGURES 25 – 27). Ornamentation of shields comprising small, irregularly distributed foveae. Sternal region: shield extending just posterior to anterior margin of coxae IV, posterior margin narrowly rounded (sometimes irregular), not fused to endopodal shields, length 111 (105–118), greatest width (between coxae II and III) 40 (36–45), with 3 pairs setae, st 4 located on striated cuticle near to posterior margin of sternal shield; st 1–4 8–11 long. Exopodal and metapodal shields: separate, extending to posterior margin of respectively coxae III and median shield; setae absent. Opisthogastric region: small, usually roughly trapezoid median shield (precise shape variable), anterior margin just posterior to coxae IV, length 26 (24–28), flanked by setae st 5 (4–6 long, mounted on small platelets) and pair of poroids; ventrianal shield rounded trapezoid, anterior margin sometimes slightly convex or irregular, 58 (55–60) long, greatest width (between anterolateral angles) 67 (61–73), with 3 pairs setae, located near anteromedian margin (8–10 long), level with anterior limit of anus and (paranals) posterolateral to anus (both 10–14 long), postanal seta inserted just anterior to cribrum, 5–6 long, 1 pair marginal poroids anterolateral to paranals; striated cuticle lateral and anterior to ventrianal shield bears 5 pairs setae, each seta mounted on platelet, anteromedian pair, at 9–10, the longest, remainder 5– 9, platelets of lateral 2 pairs largest, 1 pair poroids lateral to anteriormost setae; marginal shield represented by 2 pairs ventral platelets, each bearing 1 seta; peritrematic shields not fused to dorsal shield.

Gnathosoma. Hypostome and basis gnathosomatica: anterior and internal posterior hypostomatic setae c. 5 and 6 long respectively, external posterior hypostomatic seta 16 (14–18), palpcoxal seta 6–8. Chelicerae: fixed digit 18 (16–20) long, movable digit 14–16.

Legs. Lengths - I 104 (94–110), II 133 (125–143), III 111 (103–120), IV 126 (117–135).


In addition to the type locality, the new species has been found at the following two sites: England, South Lancashire, Tarbock Green, Prescot, Waterlane Farm (grid ref. SJ 469880View Materials), beneath leaking guttering along outer edge of Dutch barn, ex. damp rotten straw down to depths of 15 cm, coll. F.D. Monson, 1 May 2004; Barn Hey Farm (grid ref. SJ 466871View Materials), up to 0.5 metres outside open edge of Dutch barn, same habitat, coll. F.D. Monson, 30 January 2006 (specimens in second author’s collection).


The species is named in honour of Professor Gwilym O. Evans, Storrington, West Sussex, UK, to mark his contributions to uropodine systematics.


The leg trochanteral formula of 4-5 - 3 - 3, absence of seta pd 3 from barsitarsi II –IV and, respectively, four and 10 setae on the palp genu and tibia have not previously been described in uropodines or mesostigmatid deutonymphs and adults. The setal complements of trochantera I and II respectively represent the larval and deutonymphal states seen in gamasines and lower Uropodina  ( Evans 1963, 1972), while trochantera with three setae have been recorded by Hirschmann (1983). The presence of 17 setae on tarsi II –IV also occurs in protonymphal Gamasina  , but, in this instance, the basitarsi bear four throughout ontogeny and it is seta mv and not pd 3 that is added in the deutonymph to make up the adult complement ( Evans 1963).